Substrate holding structure and substrate processing device

ABSTRACT

The object of the present invention is to prevent damage due to thermal stress induced into a substrate holding table in a substrate holding structure for holding a substrate to be processed. In the substrate holding structure having the substrate holding table arranged at the top of a support column, a flanged part is defined by an inner circumferential surface and an outer circumferential surface at a joint between the support column and the substrate holding table. The inner circumferential surface is formed of an inclined surface, which is inclined such that the inner diameter of the flanged part successively increases as approaching the lower surface of the substrate holding table. On the lower surface of the substrate holding table to which the flanged part is joined, a U-shaped groove is formed so as to correspond to the outer circumferential surface of the flanged part.

TECHNICAL FIELD

The present invention relates to a substrate holding structure used forholding a substrate to be processed in a substrate processing apparatusand a substrate processing apparatus utilizing the substrate holdingstructure.

BACKGORUND ART

In a substrate processing apparatus, such as a CVD apparatus, aplasma-assisted CVD apparatus and an etching apparatus, a substrateholding structure is arranged in a processing vessel to hold a substrateto be processed. Such a substrate holding structure includes a substrateholding table for holding the substrate to be processed and a supportcolumn for supporting the substrate holding table. A heating mechanismis arranged in the substrate holding table to heat the substrate at apredetermined temperature.

In CVD apparatuses including plasma-assisted CVD apparatuses, and heattreatment apparatuses, a substrate must be heated at a temperature of400° C. or more, in some cases, 600° C. or more. With such a heating, agreat temperature gradient is generated across the substrate holdingtable.

The substrate holding table is generally made of a ceramic material,such as AlN, having excellent corrosion resistance. If thermal stress isinduced into the substrate holding table due to the temperaturegradient, the substrate holding table may possibly be damaged.

A structure for solving the above problem is disclosed inJP2002-373837A. FIG. 1 schematically shows the overall structure of asubstrate holding structure shown in JP2002-37383A. FIG. 2 schematicallyshows the vicinity of a joint between a substrate holding table and asupport column in the substrate holding structure.

Referring to FIG. 1, the substrate holding table 10 is held on thesupport column 11. The support column 11 is provided with a flanged part11A at the joint to the holding table 10. Referring to FIG. 2, thesupport column 11 is provided with a curved surface 11B at a transitionpart from a main part of the support column 11 to the flanged part 11Ato reduce thermal stress concentration at the transition part. On theflanged part 11A side of the substrate holding table 10, the substrateholding table 10 is provided with a thick joint part 10A, which isdefined by a curved surface 10B whose profile undergoes continuoustransition to the profile of the flanged part 11A.

According to the arrangement of FIGS. 1 and 2, as the parts of substrateholding table 10 other than the thick joint part 10A is thinner, anamount of heat transferred in the substrate holding table 10 is reduced.In addition, as the side surface of the thick joint part 10A is formedof a curved surface that undergoes continuous transition to the sidesurface of the flanged part 11A, thermal stress concentration at thejoint is prevented.

Note that there exist other prior-art documents relating to thistechnical field, JP2000-169268A, JP2000-290773A, JP2002-184844A,JP5-101871A and JP7-230876A.

In the aforementioned substrate holding structure disclosed inJP2002-37383A, it is necessary to grind the whole area of the backsurface of the substrate holding table 10 other than the thick jointpart 10A. However, as the substrate holding table 10 is made of aceramic material which is difficult to grind, such as AlN, the grindingof such a large area greatly increases the manufacturing cost of thesubstrate holding structure.

On the contrary, if the substrate holding table 10 is not ground in theabove manner, thermal stress due to temperature gradient induced in thesubstrate holding table 10 is concentrated on the boundary between theflanged part 11A and the substrate holding table 10, resulting in damageof the substrate holding table 10.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a substrate holdingstructure, which can be made at a low manufacturing cost and which cansuppress thermal stress concentration, and also provide a substrateprocessing apparatus employing such a substrate holding structure.

Another object of the present invention is to reduce temperaturegradient in a substrate holding table.

In order to attain the above objects, the present invention provides asubstrate holding structure, which includes a support column provided ata top end portion thereof with a flanged part, and a substrate holdingtable joined to the flanged part, wherein: the substrate holding tableincludes a heating mechanism; the substrate holding table is provided ina lower surface thereof with a U-shaped groove extending along an outercircumferential surface of the flanged part; and an innercircumferential surface of the U-shaped groove is connected to the outercircumferential surface of the flanged parts to form a continuous singleplane.

In one preferred embodiment, in sectional view, both an end portion of aprofile line of the inner circumferential surface of the U-shaped grooveon a side of the flanged part and a profile line of the outercircumferential surface of the flanged part are situated on a singleline segment extending in a vertical direction.

In one preferred embodiment, the substrate holding structure is made byjoining the flanged part and the substrate holding table to each otherafter forming them individually; and a joint surface between the flangedpart and the substrate holding table is positioned within a rangecorresponding to the single line segment extending in the verticaldirection.

In one preferred embodiment, an inner circumferential surface of theflanged part provides an inclined surface, which is inclined such thatan inner diameter of the flanged part successively increases asapproaching the lower surface of the substrate holding table.

In one preferred embodiment, a recess is formed in a part of a portion,opposing the flanged part, of the lower surface of the substrate holdingtable; and the flanged part is joined to the lower surface of thesubstrate holding table only at an outermost annular area thereof.

In one preferred embodiment, the heating mechanism includes an innerheating-mechanism part and an outer heating-mechanism part formedoutside the inner heating-mechanism part; and the innerheating-mechanism part and the outer heating-mechanism part are drivenby first and second drive power supply system both extending in thesupport column, respectively.

In this case, preferably, the substrate holding table includes first andsecond semicircular conductive patterns, which are arranged below theheating mechanism and are connected to first and second power supplylines constituting the second drive power supply system, respectively;and the first and second conductive patterns substantially cover a wholearea of the substrate holding table except for gap areas defined betweenthe first conductive pattern and the second conductive pattern.

The present invention further provides a substrate holding structureincluding a support column provided at a top end portion thereof with aflanged part, and a substrate holding table joined to the flanged part,wherein: the substrate holding table includes a heating mechanism; thesupport column includes, at a joint between the support column and thesubstrate holding table, a flanged part having an inner circumferentialsurface and an outer circumferential surface; the inner circumferentialsurface provides an inclined surface, which is inclined such that aninner diameter of the flanged part successively increases as approachingthe lower surface of the substrate holding table; the outercircumferential surface provides an inclined surface, which is inclinedsuch that an outer diameter of the flanged part successively increasesas approaching the lower surface of the substrate holding table; and theinclined surface constituting the outer circumferential surfaceundergoes continuous transition to the lower surface of the substrateholding table.

In one preferred embodiment, the lower surface of the substrate holdingtable is formed in a flat surface at a part joined to the flanged partand an area surrounding the part.

The present invention further provides a substrate processing apparatus,which includes: a processing vessel connected to an exhaust system; agas supply system that supplies a process gas into the processingvessel; and the aforementioned substrate holding structure arranged inthe processing vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view showing the constitution of aconventional substrate holding structure;

FIG. 2 is an enlarged, vertical cross-sectional view showing a part ofthe substrate holding structure of FIG. 1;

FIG. 3 is a vertical cross-sectional view schematically showing theconstitution of a substrate processing apparatus in a first embodimentof the present invention;

FIG. 4 is a vertical cross-sectional view schematically showing theconstitution of a substrate holding structure employed in the substrateprocessing apparatus of FIG. 3;

FIG. 5 is a plan view showing a heater pattern of a heating mechanismemployed in the substrate holding structure of FIG. 4;

FIG. 6 is a plan view showing a power feeding pattern of the heatingmechanism employed in the substrate holding structure of FIG. 4;

FIG. 7 is a vertical cross-sectional view showing the stressconcentration reducing constitution employed in the substrate holdingstructure of FIG. 4;

FIG. 8 (A) and (B) are charts showing distribution of thermal stressinduced in the substrate holding structure of FIG. 7 under a center-coolcondition and a center hot condition, respectively; and

FIG. 9 is a vertical cross-sectional view showing the constitution of asubstrate holding structure in a second embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION 1st. Embodiment

FIG. 3 shows the constitution of a substrate processing apparatus 20 inthe first embodiment of the present invention, while FIGS. 4 to 7 showthe constitution of a substrate holding structure 50 employed in thesubstrate processing apparatus 20 of FIG. 3.

Referring to FIG. 3, the substrate processing apparatus 20 includes aprocessing vessel 21 connected to an exhaust system (not shown) throughan exhaust port 21A. A shower head 22 is arranged at the top of theprocessing vessel 21 to discharge a process gas, which is supplied froman external gas source (not shown) through a line L, into a processingspace in the processing vessel 22 through a number of openings 22A. Asubstrate holding table 23 for holding a substrate to be processed (notshown) is disposed in the processing vessel 21 so as to oppose theshower head 22.

The substrate holding table 23 is made of a ceramic material, such asAlN, having excellent corrosion resistance, high heat conductivity, highresistivity and excellent thermal-shock resistance. The substrateholding table 23 is supported on a support column 23A made of a ceramicmaterial, such as AlN, which is the same as the material of thesubstrate holding table 23. Joining of these ceramic components 23, 23Ais preferably accomplished by solid-state welding, but may beaccomplished by solid-liquid welding or soldering. An extension part 21Bextending downward from a bottom part of the processing vessel 21. Thesupport column 23A extends through the extension part 21B, and is fixedto an end part 21C of the extension part 21B. Power supply lines 23 aand 23 b extend through the support column 23A for driving a heatingmechanism (heater) embedded in the substrate holding table 23. The powersupply lines 23 a and 23 b are drawn out through a terminal chamber 21D,which is provided at the end part 21C for inhibiting oxidation orcorrosion of the power supply lines. The terminal chamber 21D isprovided with an exhaust port 21 d for exhausting the interior of thesupport column 23A.

An opening 21E for loading and unloading of a substrate to be processedis formed in the processing vessel 21D at a level corresponding to thesubstrate holding table 23. The substrate holding table 23 is providedwith lifter pins (not shown) to lift up a substrate after beingprocessed.

The substrate holding table 23 of FIG. 3 is provided with a structurefor reducing thermal stress, which will be described later. However, forsimplicity of drawings, FIGS. 3 and 4 to 6 do not illustrate thatstructure.

FIGS. 4 to 6 show the heating mechanism embedded in the substrateholding table 23. Referring to FIG. 4, the heating mechanism includes aninner heater pattern 24A formed in the vicinity of the center of thesubstrate holding table 23 and an outer heater pattern 24B formedoutside the inner heater pattern 24A. The inner heater pattern 24A issupplied with electric power through the power supply line 23 a. Theouter heater pattern 24B is supplied with electric power through thepower supply line 23 b and a power supply pattern 24C formed below theheater patterns 24A and 24B.

FIG. 5 shows a planar arrangement of the heater patterns 24A and 24B. InFIG. 5, the heater patterns 24A and 24B are indicated by hatching. Theheater patterns 24A and 24B are made of a heat-resistant metal having athermal expansion coefficient generally equal to that of AlN forming thesubstrate holding table 23, for instance, W or Mo. The heater patterns24A and 24B can be formed by forming a film of the heat-resistant metalon the substrate holding table 23 uniformly, and subsequently patterningcutouts 24 c in the film. Alternatively, the heater patterns 24A, 24Bmay be formed by forming grooves of a predetermined pattern on thesubstrate holding table 23, and successively embedding theheat-resistant metal in the grooves. The heater pattern 24A is connectedto one of power-supply wires of the power supply line 23 a at aconnecting part 23 a in a central part of the substrate holding table23, and is connected to the other of the power-supply wires of the powersupply line 23 a at a connecting part 23 a′ in the central part of thesubstrate holding table 23. The heater pattern 24B is connected to apower-supply pattern 24C₁ connected to one of power-supply wires of thepower supply line 23 b at a connecting part 23 c, and is connected to apower-supply pattern 24C₂ connected to the other of power-supply wiresof the power supply line 23 b at a connecting part 23 c′.

Note that the profiles of the heater patterns 24A and 24B are notlimited to those shown in the drawings. As long as the calorific valuedistribution in each heater pattern is narrow, another profile, such asa spiral, of the heater patterns 24A and 24B is possible. The heatingelements are not limited to plate-shaped or film-shaped as illustrated,and may be formed of coiled resistant-heating wires.

FIG. 6 shows a planar arrangement of the power supply patterns 24C₁ and24C₂. In FIG. 6, the power supply patterns 24C₁ and 24C₂ are indicatedby hatching. As shown herein, the power supply patterns 24C₁ and 24C₂comprise semicircular conductive films. The power supply patterns 24C₁and 24C₂ can be made of the same material and the same manufacturingprocess as those of the heater patterns 24A and 24B. The power supplypatterns 24C₁ and 24C₂ may be in a form of a plate, a film or a mesh.The power supply pattern 24C₁ is connected to one of the power supplywires of the power supply line 23 b at a connecting part 23 d, while thepower supply pattern 24C₂ is connected to the other of the power-supplywires of the power supply line 23 b at a connecting part 23 d′.

In this way, with the substrate holding table 23 of this embodiment, asthe inner heater pattern 24A and the outer heater pattern 24B arerespectively supplied with electric power independently, it is possibleto minimize temperature gradient in the substrate holding table 23,reducing the possibility of damage, such as cracking, due to thetemperature gradient. In addition, as the temperature of the inner areaand the outer area of the substrate holding table 23 can be controlledindependently, process uniformity in processing a substrate is improved.Note that when supplying the heater patterns 24A and 24B with electricpower, the power supply patterns 24C₁ and 24C₂ are also heated up.Nevertheless, since the power supply patterns 24C₁ and 24C₂ are arrangedgenerally over the whole area of the substrate holding table 23, thetemperature gradient in the substrate holding table 23 derived from theheating of the power supply patterns 24C₁ and 24C₂ is minimized.

FIG. 7 shows a structure for reducing thermal stress, which is employedin the substrate holding table 23 of FIG. 3. Referring to FIG. 7, thesupport column 23A for supporting the substrate holding table 23includes a flanged part 23B provided at the top end of the supportcolumn 23A and a cylindrical main body having outer diameter d arrangedbelow the flanged part 23B. Each of the substrate holding table 23 andthe support column 23A is substantially a “body of rotation (a bodyobtained by rotating a plane about an axis)” in geometrical terminology.

Formed in a lower surface 231 of the substrate holding table 23 is anannular groove 23U having a U-shaped cross section (referred to as“U-shaped groove 23U” hereinafter). The U-shaped groove 23U is definedby an inner circumferential surface 23U₁, an outer circumferentialsurface 23U₂, and a bottom surface 23U₃ connecting the innercircumferential surface 23U₁ and the outer circumferential surface 23U₂.The inner circumferential surface 23U₁ is smoothly connected to thebottom surface 23U₃ through a curved surface having a curvature radiusR₁. The outer circumferential surface 23U₂ is smoothly connected to thebottom surface 23U₃ through a curved surface having the same curvatureradius R₁. The curvature radius R₁ is smaller than depth D of theU-shaped groove 23U. A profile line of an outer circumferential surface23B₁ of the flanged part 23B extends in a vertical direction. A profileline of the inner circumferential surface 23U₁ of the U-shaped groove23U extends on an extension of the profile line of the outercircumferential surface 23B₁ in the vertical direction. That is, theprofile line of the outer circumferential surface 23B1 and the profileline of the inner circumferential surface 23U₁ form a single,continuous, straight line (line segment) extending in the verticaldirection, so that no step exists at a connecting point P between theprofile lines. That is, the outer circumferential surface 23B₁ and theinner circumferential surface 23U₁ form a singe, continuous, curvedsurface having a cylindrical shape in the vicinity of a joint surface235 (connecting point P) between the substrate holding table 23 and thesupport column 23A. The profile line of the curved surface having thecurvature radius R₁ is in a form of an arc, which arc starts from apoint P′, which is located a predetermined distance upwardly apart fromthe connecting point P, and which arc centers on a point O in level withthe point P′ and has a center angle of 90 degrees. According to thisconstitution, a region where the maximum thermal stress is induced islocated at a region corresponding to the curved surface having thecurvature radius R₁. In other words, the region where the maximumthermal stress is induced is located at a region other than the jointsurface 235 (connecting point P) between the substrate holding table 23and the support column 23A having a low material strength.

If this substrate holding structure 50 is intended to be used for a 300mm diameter wafer, respective dimensions of the structure are, forexample, as follows: about 340 mm in diameter of the substrate holdingtable 23; 19 mm in thickness of the table 23; about 56 mm in diameter dof the main body of the support column 223A; about 86 mm in diameter ofthe outer circumferential surface 23B₁ of the flanged part 23B of thesupport column 223A; about 5 mm in width W of the U-shaped groove 23U;about 2.5 mm in depth D of the U-shaped groove 23U; and about 2.5 mm incurvature radius R₁. It will be understood from the above that theamount of grinding for forming the U-shaped groove 23U is remarkablysmall. As the substrate holding table 23 is made of a ceramic materialdifficult to grind, the reduced grinding amount results in a greatlyreduced manufacturing cost of the substrate holding table 23 and thusthe substrate holding structure 50

Note that preferable dimensions of respective parts of the substrateholding table 23 are as follows:

Distance from point P to point P′: 0.1-0.5 mm, more preferably, 0.5-1mm;

Curvature radius R₁: 0.5-5 mm, more preferably, 1-3 mm;

Width W of U-shaped groove 23U: 1-20 mm, more preferably, 5-10 mm; and

Depth D of U-shaped groove 23U: 1-10 mm, more preferably, 1-5 mm.

Although the U-shaped groove 23U in the embodiment of FIG. 7 has thebottom surface 23U₃ extending horizontally, the present invention is notlimited thereto. As shown by broken lines on the right side of FIG. 7,an inner circumferential surface 23U₁ may be connected to the outercircumferential surface 23U₂ through a surface 236 having a singlecurvature radius.

An annular groove 232 is formed in the lower surface 231 of thesubstrate holding table 23. The depth of the groove 232 need not be solarge, and may be about 1 mm. Due to the provision of the groove 232, agap is defined between an upper surface 234 of the flanged part 23B ofthe support column 23A and the substrate holding table 23, so that thearea of the joint surface 235 between the substrate holding table 23 andthe support column 23A is reduced. As a large temperature differenceexists between the substrate holding table 23 with a built-in heatingmechanism and the support column 23A without including any heatingmechanism, if the area of the joint surface 235 is too large, thermalstress induced in the vicinity of the joint surface 235 becomes larger.In addition, if the area of the joint surface 235 is too large, thecalorific value flowing from the substrate holding table 23 to thesupport column 23A becomes large, deteriorating the temperatureuniformity of the substrate holding table 23. In order to avoid suchproblems, the width of the joint surface 235 is set to be a value (e.g.,4 mm) as small as possible, as long as sufficient joint strength betweenthe substrate holding table 23 and the support column 23A can beensured. Note that the U-shaped groove 23U and the annular groove 232are formed by grinding the flat lower surface 231 of the substrateholding table 23 arranged in a single horizontal plane. The jointsurface 235 is positioned outside a cylinder which is coaxial with thesupport column 23A and has a diameter equal to the diameter d of thesupport column 23A.

An inner circumference of the flanged part 23B is in a form of aninclined surface 23 f, whereby thermal stress concentration thereto isreduced. A curved surface 23R having a curvature radius R₂ is formed ata transitional part, from the main body to the flanged part 23B, of thesupport column 23A, whereby thermal stress concentration thereto isreduced.

FIG. 8(A) shows stress distribution in the substrate holding structureof FIG. 7 when the substrate holding structure 23 shows so-called“center-cool” temperature gradient, where the temperature of the centerpart is low while the temperature of the peripheral part is high.Alphabets attached to respective areas denote various levels of stress:“A” designates an area with a stress exceeding +6.79 kgf·mm⁻²; “B”designates an area with a stress of 5.43˜+6.79 kgf·mm⁻²; “C” designatesan area with a stress of +4.07˜+5.43 kgf·mm⁻²; “D” designates an areawith a stress of +2.71˜+4.07 kgf·mm⁻²; “E” designates an area with astress of +1.35˜+2.71 kgf·mm⁻²; “F” designates an area with a stress of0˜+1.35 kgf·mm⁻²; and “G” designates an area with a stress of −1.37˜0kgf·mm⁻². Note that a positive value represents a tensile stress, whilea negative value represents a compressive stress.

Referring to FIG. 8(A), as the center part of the substrate holdingtable 23 is contracted in comparison with the peripheral part under sucha “center-cool” condition, a large tensile stress tends to be induced inthe table 23, particularly, at a position thereof corresponding to theouter circumferential surface 23B₁ of the flanged part 23B. However, itis found that the stress concentration is remarkably reduced due to theprovision of the U-shaped groove 23U at a position corresponding to theouter circumferential surface 23B,. In the state shown in FIG. 8(A), itwill be understood that the maximum tensile stress (the value exceeding8.15 kgf·mm⁻²) appears in the curved surface part having curvatureradius R1 in the U-shaped groove 23U (see an arrow labeled “MAX”). Itshould especially be noted that the stress concentration does not appearin the joint between the substrate holding table 23 and the supportcolumn 23A.

FIG. 8(B) shows stress distribution under so-called “center-hot”condition, where the temperature of the center part of substrate holdingtable 23B is high while the temperature of the peripheral part is low.In this case, it is found that little thermal stress concentrationappears in the vicinity of the joint between the substrate holding table23 and the support column 23A.

As mentioned above, with the substrate holding structure in thisembodiment, the thermal stress concentration can be reduced whileminimizing a grinding amount of the lower surface of the substrateholding table (see and compare with the prior art of FIGS. 1 and 2). Inaddition, as the heaters 24A and 24B are driven independently of eachother, the temperature gradient in the substrate holding table 23 can beminimized. Consequently, it is possible to manufacture a substrateholding structure, which is reliable and has no risk of failure, at alow cost.

2nd. Embodiment

FIG. 9 shows a constitution of a substrate holding structure in thesecond embodiment of the present invention. In FIG. 9, component partsidentical to those in the first embodiment are designated by the samereference signs, and duplicate description thereof are omitted.

Referring to FIG. 9, the substrate holding structure 40 of the secondembodiment has a structure similar to the substrate holding structure 20of the first embodiment, however, the former mainly differs from thelatter in that an outer circumferential surface of the flanged part 23Bof the support column 23A is in a form of an inclined surface 33B₁inclined such that the diameter of the outer circumferential surfacegradually increases as approaching the lower surface of the substrateholding table 23.

A profile line of the inclined surface 33B₁ is curved so that itundergoes continuous transition to the profile line of the lower surfaceof the substrate holding table 23. In other words, the inclination of atangential line of the profile line with respect to a horizontal planegradually becomes close to 0 degree as approaching the lower surface ofthe substrate holding table 23. Consequently, there exists no step whichcauses stress concentration at a part between the outer circumferentialsurface 33B₁ and the lower surface of the substrate holding table 23.

According to this embodiment, as it is unnecessary to grind the lowersurface of the substrate holding table 23, the manufacturing cost of thesubstrate holding structure is further reduced.

Also in this embodiment, by driving the heaters 24A and 24Bindependently of each other, it is possible to minimize the temperaturegradient in the substrate holding table 23, and thus generation ofthermal stress itself can be restrained.

In the above description, the substrate holding structure 20 or 40 isused in the CVD apparatus of FIG. 3. However, the invention is notlimited to thereto, and the same structure is generally applicable tovarious substrate processing apparatuses, for example, a plasma-assistedCVD apparatus, a heat treatment (RTP) apparatus, an etching apparatus,and so on.

The description has been made for preferred embodiments of the presentinvention. However, the invention is not limited to the above-mentionedembodiments, and various changes and modifications are possible withinthe scope of claims.

1. A substrate holding structure comprising a support column provided ata top end portion thereof with a flanged part, and a substrate holdingtable joined to the flanged part, wherein: the substrate holding tableincludes a heating mechanism; the substrate holding table is provided ina lower surface thereof with a U-shaped groove extending along an outercircumferential surface of the flanged part; and an innercircumferential surface of the U-shaped groove is connected to the outercircumferential surface of the flanged parts to form a continuous singleplane.
 2. The substrate holding structure according to claim 1, whereinin sectional view, both an end portion of a profile line of the innercircumferential surface of the U-shaped groove on a side of the flangedpart and a profile line of the outer circumferential surface of theflanged part are situated on a single line segment extending in avertical direction.
 3. The substrate holding structure according toclaim 2, wherein: the substrate holding structure is made by joining theflanged part and the substrate holding table to each other after formingthem individually; and a joint surface between the flanged part and thesubstrate holding table is positioned within a range corresponding tothe single line segment extending in the vertical direction.
 4. Thesubstrate holding structure according to claim 1, wherein an innercircumferential surface of the flanged part provides an inclinedsurface, which is inclined such that an inner diameter of the flangedpart successively increases as approaching the lower surface of thesubstrate holding table.
 5. The substrate holding structure according toclaim 1, wherein: a groove is formed in a part of a portion, opposingthe flanged part, of the lower surface of the substrate holing table;and the flanged part is joined to the lower surface of the substrateholding table only at an outermost annular area thereof.
 6. Thesubstrate holding structure according to claim 1, wherein: the heatingmechanism includes an inner heating-mechanism part and an outerheating-mechanism part formed outside the inner heating-mechanism part;and the inner heating-mechanism part and the outer heating-mechanismpart are driven by first and second drive power supply system bothextending in the support column, respectively.
 7. The substrate holdingstructure according to claim 6, wherein: the substrate holding tableincludes first and second semicircular conductive patterns, which arearranged below the heating mechanism and are connected to first andsecond power supply lines constituting the second drive power supplysystem, respectively; and the first and second conductive patternssubstantially cover a whole area of the substrate holding table exceptfor gap areas defined between the first conductive pattern and thesecond conductive pattern.
 8. The substrate holding structure accordingto claim 1, wherein the substrate holding table and the support columnare made of ceramics.
 9. A substrate processing apparatus comprising: aprocessing vessel connected to an exhaust system; a gas supply systemthat supplies a process gas into the processing vessel; and thesubstrate holding structure, as defined in claim 1, arranged in theprocessing vessel.
 10. A substrate holding structure comprising asupport column provided at a top end portion thereof with a flangedpart, and a substrate holding table joined to the flanged part, wherein:the substrate holding table includes a heating mechanism; the supportcolumn includes, at a joint between the support column and the substrateholding table, a flanged part having an inner circumferential surfaceand an outer circumferential surface; the inner circumferential surfaceprovides an inclined surface, which is inclined such that an innerdiameter of the flanged part successively increases as approaching thelower surface of the substrate holding table; the outer circumferentialsurface provides an inclined surface, which is inclined such that anouter diameter of the flanged part successively increases as approachingthe lower surface of the substrate holding table; and the inclinedsurface constituting the outer circumferential surface undergoescontinuous transition to the lower surface of the substrate holdingtable.
 11. The substrate holding structure according to claim 11,wherein the lower surface of the substrate holding table is formed in aflat surface at a part joined to the flanged part and an areasurrounding the part.